The Id attribute of a ListInstance feature is ignored by SharePoint

A developer asked me today why SharePoint doesn’t use the Id specified in the ListIntance feature manifest for the guid of the list to be created. I checked the MSDN documentation and found out that the Id should be actually an integer number rather than a Guid: http://msdn.microsoft.com/en-us/library/ms476062.aspx

Looking at the SharePoint code with reflector revealed that the class that is responsible for activating a ListInstance feature is Microsoft.SharePoint.SPListInstanceElement which actually completely ignores the Id attribute. It creates the list the “normal” way and the list instances will always come with a different and unique guids.

internal SPList Microsoft.SharePoint.SPListInstanceElement.EnsureListExists(SPWeb web)

{

    SPList list2;

    try

    {

        return web.Lists[this.Title];

    }

    catch (ArgumentException)

    {

        Guid guid;

        int num;

        string str;

        string documentTemplate;

        SPListTemplate.QuickLaunchOptions off = SPListTemplate.QuickLaunchOptions.Off;

        if (string.IsNullOrEmpty(this.TemplateType))

        {

            return null;

        }

 

      …

 

        num = int.Parse(this.TemplateType, NumberFormatInfo.InvariantInfo);

        str = base.FeatureDefinition.Id.ToString();

        documentTemplate = null;

      

        guid = web.Lists.Add(this.Title, this.Description, this.Url, str, num, documentTemplate, off);

        if (!(guid != Guid.Empty))

        {

            return null;

        }

        return web.Lists[guid];

 

    }

}